Fractional distillation



Patented Apr. 2, 1929.

UNITED "STATES JOHN PRIMROSE, OF RICHMOND, NEW YORK, A SSIGNOR 'I'O FOSTER WHEELER COR- PORATION, OF NEW YORK, N. Y.,

1,707,369 PATENT OFFICE.

A CORPORATION OF NEW YORK.

FRACTIONAL DISTILLATION.

Application filed January 30, 1924. Serial No. 689,404.

My present invention consists in an improved method of distillation, especially devised and adapted for use in the fractional distillation of mineral oil.

The general object of the present invention is to provide a method of fractional distillation which canbe carried out with a desirable heat economy and by means of rel atively simple and effective apparatus, and

{O in particular with an oil heater directly heated by fire and which will insure clean cuts or distillation fractions and will avoid crackin the oil treated. In carr a y ing out my invention, I gradually raise the temperature of the oil treated up to the maximum temperature required by a continuous circulation of the, oil through a closed circulating system comprising a fire heated tubular oil heater'and a reservoir or tank, with such velocity of oil flow through the oil heater relative to the rate of heat absorption in the heater as will avoid a difference between the temperatures at which the oil enters and leaves the heater in excess of a predetermined and relatively small amount. The difference between the temperature of the oil entering and the temperature of the oil leaving the heater which it is desirable to maintain will vary with the conditions of .use. In some cases it will be desirable to prevent this temperature differential from exceeding F while in'other cases it may well be as high as F. In general it must be kept low enough to insure clean distillation, cuts and the avoidance of cracking, but on the other hand it should be high enough to insure a desirably rapid heating of the oil undergoing treatment with apparatus of relatively small bulk and without putting an unduly heavy load on the circulating pump or requiring an undesirably high pressure at the pump outlet to maintain the desired velocity of flow.

The oil vapors generated are Withdrawn from the circulating system as they are produced in the gradual heating up of the oil. The vapors may be withdrawn through the vapor outlet of a suitable oil and vapor 50 separating tower receiving oil and vapor from the oil heater and returning the unvaporized oil to the storage reservoir, or the oil or vapor may be passed directly into the storage reservoir and the latter be provided with a suitable outlet for vapors. In either case, the vapors, after being withdrawn, may be treated in any usual or suitable mannor to separate the desired fractions and to condense their condensable' constituents. The invention not only insures clean eut distillation fractions, but also insures a desirably homogeneous liquid residue contain ing practically no free carbon, which is especially important when the'invention is employed for the primary purpose of producing cylinder oil, a purpose for which the invention is especially well adapted. A characteristic advantage of the invention is that it permits of the safe and satisfactory use of the simplest and'most effective form of oil heater, namely: a tubular fire heated oil heater, without over-heating and thereby cracking the oil, which would reduce the quantity and impair the purity of the vaporized products, and would cause injury to the heater as the result of carbon deposits there- 1n.

In the accompanying drawings I have illustrated somewhat diagrammatically aps paratus well adapted for use in carrying out the invention.

Of the drawings Fig. '1 is a diagrammatic elevation of apparatus including a separating tower separate from the storage reservoir; and

Fig. 2 is an elevation of a portion of a modified arrangement in which the oil and vapor are returned from the heater directly to the storage tank.

In the apparatus shown in Fig. 1, A represents an oil heater, comprising a combustion chamber A shown as adapted to be heated by the combustion of oil supplied at A The rear wall ofthe combustion chamber is formed by a bridge wall A over which the 9 products of combustion pass into the upper end of the furnace chamber A from the bottom of which they pass out to the stack through the outlet A In the chamber A are arranged a bank of tubular elements B, which may well be of the Foster type, i. e.,

vtubes surrounded by cast iron tubular casing elements externally corrugated to increase the heat absorbing surface. q

The oil to be heated passes into the tubular elements B at the bottom of the tank from a supply header 0, and passes back and forth through the tubes B at successively higher levels until it reaches the vertical pipes D, through which it passes into tubular elements E mounted in the roof of the furnace and from which the oil passes out of the heater proper into a header EH With the type of heater described, the elements E are heated mainly by radiation, and the portions of those tubes above the combustion chamber A and bridge wall A3 are advantageously surrounded by easing parts E. The tubular elements B are heated mainly by contact with and conduction from the heating gases, while the tubes D are heated partly by radiation and partly by contact with the heating gases. I

Oil is supplied to the heater inlet header C from a storage reservoir or tank G by a circulating pump H, which draws oil from the bottom of the tank. The oil and any vapors mixed therewith, pass from the heater outlet header E through a pipe F into an oil and vapor separating tower I, which may be of any usual or suitable form and is provided at its upper end with a vapor outlet I, through which the vapors separated from the oil are discharged. The vapors thus given off will vary with the temperature of the oil as the latter is gradually raised. At its lower end the tower I is connected to the top of the storage tank G by a pipe connection I which should be of a character to permit the passage into the tower of vapors liberated in the storage tank, as well as to permit the down-flow of oil from the tower into the tank. To facilitate the desired evaporation, provisions are advantage ously made for injecting steam at a suitable temperature into the vapor space of the tower, as through the inlet I and into the storage reservoir G as by means of the perforated pipe K located in the tank near the bottom of the latter, so as to be normally submerged in the oil held in the tank.

The apparatus shown is charged with the oil to be treated through supply piping L, which, in the form of the apparatus shown in Fig. 1, comprises a separate valved outlet L to the separating tower and to the storage tank G. From time to time, the unevapo rated-"liquid residue may be withdrawn from the system as by means of the valved pump outlet I-I.

While the oil heater illustrated and described, is of a type and form well adapted for use in carrying out the invention, it will be understood that many different forms of oil heaters can be employed. Moreover, as already indicated, the use of a separating tower is not essential to the practice of the invention, and in Fig. 2 I have illustrated a form of apparatus which may be used in carrying out my invention and which differs from that shown in Fig. 1 in that the aromas separating tower is omitted and the pipe F discharges oil and vapor directly into the storage tank Gr through a normally submerged perforated pipe F. In this apparatus, all of the vapor generated and separated from the oil is discharged from the storage tank through the outlet G at the top of the latter.

While my invention was primarily devised and is especially well adapted for use in the fractional distillation of mineral oil, it may be used in analogous operations, as in distilling vegetable oils and crude coal tar, dehydrating oil, distilling oil without fractionation as in recovering gasoline from absorption oil in casing head absorption plants, and the re-running of distillates to recover the desired end points now usually done in steam stills. In dehydrating oil, the invention possesses the advantage that with the gradual heating up of the oil and water mixture, the water is driven off at a uniform rate and withoutthe puking action characteristic of dehydration in a tank still.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In distilling oil, the method which consists in circulating a closed system comprising a storage tank and a fire heated tubular oil heater with such velocity of flow through the oil heater relative to the heat absorption capacity of the oil heater as to gradually raise the average temperature of the oil in the system without heating the oil to a cracking temperature, and withdrawing the different Vapors successively liberated at successively higher temperatures as the batch of oil is progressively heated up.

2. In fractionally distilling oil, the method which consists in circulating a batch of oil through aclosed system comprising a storage tank and a fire heated tubular foil heater with such velocity of flow through the oil heater as to gradually raise the average temperature of the oil in the system so as to keep the difference between the temperature at which the oil enters the heater and the temperature at which the oil leaves the heater small enough to permit the formation of relatively clean distillation cuts and not in excess of a predetermined and relatively small amount, and withdrawing'the different vapor fractions successively liberated at succesively high temperatures as the batch of oil is progressively heated up.

Signed at New York in the county of New York and State of New York this 22nd day of January, A. D. 1924.

JOHN PRIMROSE.

batch of oil through a 

